Carbon black reinforcement for tire treads conventionally provides a suitable increase in electrical conductivity for the rubber composition to dissipate buildup of static electricity from the vehicle to the road as well as a suitable increase in thermal conductivity to reduce the heat buildup in the tire tread during its use under working conditions.
However, it is sometimes desired to utilize a rubber composition for a tire tread where its reinforcement is substantially silica with an accompanying substantial reduction in the content of carbon black reinforcement. As a result, electrical conductivity as well as thermal conductivity of the tire tread rubber composition may be somewhat compromised.
For example, reinforcing filler in an amount of about 35 to about 80, or sometimes more, phr is often used for a tire tread rubber composition. A threshold of about 35 or 40 phr of carbon black is usually sufficient for most purposes to provide adequate electrical conductivity for static electricity and thermal conductivity for heat dissipation for a tire tread rubber composition. However, when a substantial portion of the reinforcing filler is silica with an attendant reduction in the quantity of carbon black, such as, for example, less than the aforesaid about 35 phr of carbon black, the tread's electrical conductivity and thermal conductivity may both be compromised.
Indeed, such a quantitatively silica reinforced tire tread having, for example, a content of at least 40 phr of silica and 25 phr or less carbon black may have a volume electrical resistivity of 10 to the 12th ohm-cm or more. Such volume electrical resistivity may suitably be determined by DIN 53682 or ASTM Method D257-92.